The present invention relates to the type of thermosetting resin composition that is used broadly in the field of electric and electronic appliances; and, more particularly, the invention relates to a solvent-free thermosetting resin composition, a process for producing the same, and a product thereof, that is required, from the viewpoint of workability, to be in a liquid form before curing.
The present invention relates to a liquid sealing material and paste bonding material for mounting semiconductors and to the conductive paste material that is used for connecting the layers of a printed wiring board, all of which are used broadly in the field of electronic appliances. The resins used for these materials are required to have a filling ability with a filler and metallic powder and an ability to impregnate into glass cloth.
The resin, after being cured, on the other hand, is required to have high-temperature mechanical properties, so that the resin can be used at a high temperature during the mounting of components or in operation. Conventionally, an epoxy resin composition, which is in a liquid form at room temperature (25° C.), has been used broadly in this field, and a reactive diluent, such as phenyl-glycidyl-ether, is added to lower the viscosity of the varnish. Besides, for a curing agent, a liquid acid-anhydride type is used to lower the viscosity of the varnish. However, when a low molecular-weight component, such as butyl-glycidyl-ether or phenyl-glycidyl-ether, is used as the diluent, the material properties of the cured resin, particularly those at a high temperature, tend to deteriorate (“New Epoxy Resin” written by Hiroshi Kakiuchi, Article 9, 1988).
When liquid acid-anhydride is used as the curing agent, the amount needed is the same as the epoxy, and its applications are limited in view of the material properties, curing ability and workability (“Higher Performance of Epoxy Resin, and Mixing Technique, Evaluation, and Application of Curing Agent: Section 3” written by Technical Information Association, 1997).
In addition, since an applicable epoxy resin is limited to a low molecular-weight alicyclic type epoxy resin, such as vinyl-cyclohexene-dioxide (25° C., 7 cps) or alicyclic epoxy-carbonate (25° C., 360 cps), restraints arise in the material properties in that an amine type curing agent cannot be used due to its reactivity, the cured resin is brittle, and so on.
For this reason, aromatic liquid epoxy resins of a bisphenol A or bisphenol F type or a phenol-novolak type, which have excellent mechanical properties, bonding ability and heat resistance after being cured, have been used. However, since these resins have high viscosity at around room temperature (25° C.), lower viscosity is attained by using both an alicyclic type epoxy resin and a reactive diluent, or by using a liquid acid-anhydride type curing agent at the sacrifice of the material properties of the cured resin.
On the other hand, as methods of improving the mechanical properties of the resin at a high temperature, the Japanese Application Patent Laid-Open Publication No. Hei 8-100107 (1996) discloses a polycondensation of the resin by adding metallic alkoxide to an epoxy resin; Japanese Application Patent Laid-Open Publication No. Hei 9-216938 (1997) discloses polycondensation of the resin after swelling a metallic alkoxide in a phenol resin; and Japanese Application Patent Laid-Open Publication No. Hei 9-291131 (1997) discloses condensation of the resin by a sol-gel method after adding metallic alkoxide into a polyurethane resin. However, since the curing reaction involves polycondensation in these methods, there arises a problem in that water is generated during the reaction and blistering is caused on the interface of the compound material. Besides, in these prior methods, no consideration is given to the prevention of blistering and cracking caused on the interface of the compound material by a change in the temperature.
The Japanese Application Patent Laid-Open Publication No. Hei 8-199045 (1996) discloses a method where, in order to reduce the generation of thermal stress, alkoxyl silane and water are added to the epoxy resin dissolved in an organic solvent; and, after the alkoxyl group in alkoxyl silane is hydrolyzed, the solvent is removed, and then the resin is heated to cure it and to dehydrate and condensate the hydroxyl group. However, since water is generated in the curing process, this method leads to deficiencies, such as creation of a void.
It is indicated in Japanese Application Patent Laid-Open Publication No. Hei 5-291438 (1993), which relates to a semiconductor device in which the semiconductor is sealed using an epoxy resin composition comprising epoxy resin, a curing agent and a reaction product of silane, that the resin composition increases the bonding ability of the semiconductor device with the frame and the silicon chip, and increases the moisture resistance and the reliability of the semiconductor device. This method, however, does not refer to the preliminary reaction of the silane compound in the epoxy resin, nor to the lowered viscosity of the resin.
It is indicated in Japanese Application Patent Laid-Open Publication No. Hei 11-209579 (1999), which relates to an epoxy resin composition for sealing, comprising epoxy resin, a curing agent and a reaction product of silane, and containing a silane compound that contains a mercaptyl group, that the bonding ability of the resin composition can be improved when the silane compound containing a mercaptyl group is first hydrolyzed and then reacted with the epoxy resin. However, the mixture of the silane compound containing a mercaptyl group is 0.001 to 5% by weight, and the invention does not refer to the realization of a lower viscosity by forming organosilicon compound polycondensates having a degree of polycondensation of 2 or higher.
Conventionally, to lower the viscosity of liquid thermosetting resins, there have been several methods using a reactive diluent, a liquid acid-anhydride type curing agent, or an alicyclic low molecular-weight resin. These methods, however, have caused a problem in that the material properties of the cured resin need to be sacrificed.
It is an object of the present invention to provide a solvent-free thermosetting resin composition which has a low viscosity and gives a cured resin having intact material properties, especially intact high-temperature mechanical properties, a process for producing the resin composition, and a product obtained by applying the composition.